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In: 5 A mole is a large number used for denoting a certain amount of molecules, atoms, and quantum particles. It is defines as a number equal to the number of atoms in 0.0012 kilograms of carbon 12, or ~6.022×1023. This number is also known as ~~Avogrado’s~~ Avogadro’s Number. Moles are typically used when addressing something about one specific element, such as molecular weight. A ‘mole’ is a unit used by chemists as a convenient way to count atoms. One mole of atoms contains a specific number of atoms- (6 x 10^23 to be exact) which is known as The Avogadro Number.

This number is used because if you could count out this many carbon atoms, the weight of carbon you would have would be 12g.

A mole of a molecular compound will always have a mass that is equal to its Relative Formula Mass. So a mole of water (RLM = 18) has a mass of 18g. A mole of carbon dioxide (RLM = 44) has a mass of 44g.

Moles are therefore a useful way to understand and measure elements and compounds within chemistry. A mole is to Avogadro’s number as a dozen is to twelve.

If I have twelve eggs, I have _a dozen_ eggs. If I have twelve water molecules, I have _a dozen_ water molecules.

If I have Avogadro’s number of water molecules, I have _a mole_ of water.

OK, so what’s the use of that? Well, chemical reactions happen in simple ratios. If I have two hydrogen molecules (two H2) and one oxygen molecule (one O2), I can react them and get two water molecules (two H2O). Similarly, I could take _two dozen_ hydrogen molecules and _one dozen_ oxygen molecules and react them to get _two dozen_ water molecule. I could do the same reaction with _two moles_ of hydrogen and _one mole_ of oxygen.

What makes moles useful is that they are useful for converting between grams and numbers of molecules. Let’s take a helium atom as an example. Helium typically has two protons and two neutrons in its nucleus. Protons and neutrons have roughly the same mass, so for our purpose, we’ll group them together and call them _nucleons_. That means a helium atom has four _nucleons_. Since it has four nucleons, that means one mole of helium weighs four grams. That’s it. That’s the secret. Take any atom or molecule, count all the nucleons, and you know how many grams one mole of that material is. Once you know that, you can do a bit of math to measure out the correct amounts of things to do the chemical reactions you want.